How to optimize battery life or usage

Optimized Battery Charging is enabled from the start. But you can find the function here:

Settings → Battery → Battery Health & Charging → Optimized Battery Charging

You can find more useful information here:

About Optimized Battery Charging on your iPhone - Apple Support

Yopu can find that option in Settings>Battery>Optimized Battery Charging = ON

In addition to the support article that led you here, I suggest that you take a look at these ones:--> Batteries - Maximizing Performance - Apple and/or:--> When to charge your iPhone or iPad - Apple Community

Regards

Giulio